Ongoing Research

Larval Dispersal Model:

Principal investigators: Dr. R. Cowen, Dr. C. Paris, and Dr. Srinivasan.

Population Connectivity

Theoretical studies suggest that population connectivity (the exchange of individuals among geographically-separated sub-populations that comprise a metapopulation) plays a fundamental role in local and metapopulation dynamics, community structure, genetic diversity, and the resiliency of populations to human exploitation. Recent studies have suggested that the scale of larval dispersal may be smaller than generally thought, particularly within ecologically relevant time scales. A mechanistic understanding of marine population connectivity requires resolution of the biological and physical processes involved in larval dispersal and transport. Our lab has been studying population connectivity from a variety of approaches: 1) direct empirical measurement of the processes that contribute to larval dispersal; 2) examination of population genetic structure as a means of identifying the scale of exchange over ecological time-scales, and 3) bio-physical modeling to determine the typical dispersal distances, pathways and critical factors influencing larval dispersal.

Caribbean Connectivity Study

To address the population structure of reef fishes in the Caribbean , we are taken a spatially realistic metapopulation modeling approach. One of the most fundamental structural properties of a metapopulation is the pattern of dynamical interactions between locally breeding subpopulations that determines the degree of their interconnectedness. For benthic marine populations that have a pelagic larval stage, such as most coral reef fish species, spatial dynamics can influence these interactions mainly via larval dispersal. In the Caribbean , coral reef habitat is largely spatially heterogeneous, with fragmented shallow water patches separated by deep water gaps between islands and coastlines, representing a complex landscape. The degree to which such a landscape facilitates or impedes movement among reefs is mainly driven by oceanographic regimes at various scales (i.e., daily to interannual variability in coastal and oceanic currents among coral reef patches). Connectivity can be estimated from passive transport of virtual floats (or particles) within currents derived from oceanic and coastal models. However, connectivity among marine populations can only be estimated by the probability of successful dispersal, which is largely a function of species-specific life history traits (e.g., adult productivity, spawning time and location, larval duration, larval behavior and mortality rate, settlement habitat preferences). A numerical biophysical model has been developed (link to Larval Dispersal Model ) to generate quantitative estimates of larval dispersal patterns, effective geographical dispersal distances, and ecologically significant levels of recruitment within and among regions in the Caribbean. The results of this study establish robust ecological criteria for management and conservation of coral ref fish populations via the design of networks of marine protected areas in the Caribbean .

Larval Dispersal Model:

In the context of the connectivity project, an offline Lagrangian code module has been developed to track the trajectory of individual particles (larvae) from selected spawning locations as a function of time. The motion is assumed to be forced by the underlying velocity field of the fluid medium. The particles are released within the coastal ocean and are moved along using model-generated velocity fields by a 4 th order Runge-Kutta integration of the Ordinary Differential Equation. Additionally, at each time step a random displacement is added to the particles to parameterize the effects of the physical processes occurring at length scales smaller than the resolution of the ocean model. The particles are essentially independent of each other and therefore the model is a good candidate for parallel computation. The parallel implementation of this model uses a master-slave paradigm in which the master process reads in the number of particles and distributes a set of these particles to the slave nodes. Each slave node accesses the velocity data from the data files independently and moves the particles for a specified time interval and, when finished, requests more work from the master. This parallel code exhibits a nearly linear scalability and is suitable for high throughput computations.

Billfish Research:

Principal investigators: Dr. R. Cowen, Dr. K. Leaman, Dr. D. Olson, Dr. S. Smith, and Dr. S. Sponaugle.

PhD. Students: Dave Richardson and Joel Llopiz.

Technicians: Peter Lane, Cedric Guigand, Aki Shiroza, Peter Vertes, Kelly Denit.

This NSF-funded, multi-disciplinary project, started in January 2003. Its primary objectives are 1) to indentify the sources of the three distinct larval billfishes patches within the Straits of Florida (S0F); 2) determine how these patches differ in terms of the trophic and growth environment of the billfish larvae, and 3) investigate the transport fates of larval billfishes from these differrent patches . The monthly field data collection consists of ichthyoplankton, and plankton tows, CTD, fluorometry, and ADCP measurements over a three year period. Ichthyoplankton collection and circulation patterns will be linked, via otolith work, to estimate spawning locations.